OFFSET
1,1
COMMENTS
A matrix over GF(2) is an ortho-projection if and only if the matrix is symmetric and idempotent. A labeled ortho-projection graph is a labeled, undirected pseudograph without multiple edges and without multiple loops whose adjacency matrix is an ortho-projection matrix over GF(2). These matrices and graphs arise naturally in low-dimensional topology.
REFERENCES
B. Shtylla and L. Zulli, Ortho-projection graphs, in preparation.
LINKS
L. Zulli, Home Page [broken link]
EXAMPLE
a(2)=4 because there are four 2 X 2 ortho-projection matrices over GF(2), namely [0 0 / 0 0], [0 0 / 0 1], [1 0 / 0 0], [1 0 / 0 1].
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
B. Shtylla and L. Zulli (shtyllab(AT)lafayette.edu, zullil(AT)lafayette.edu), Mar 05 2003
EXTENSIONS
a(9) from Louis Zulli (zullil(AT)lafayette.edu), Aug 23 2004
STATUS
approved